ci: Add native PowerPC64LE and s390x jobs

We now have access to native runners, so make use of them for these
architectures. The existing ppc64le Docker job is kept for now.

library/compiler-builtins/.github/workflows/main.yaml

@@ -70,8 +70,12 @@ jobs:
           os: ubuntu-24.04
         - target: powerpc64le-unknown-linux-gnu
           os: ubuntu-24.04
+        - target: powerpc64le-unknown-linux-gnu
+          os: ubuntu-24.04-ppc64le
         - target: riscv64gc-unknown-linux-gnu
           os: ubuntu-24.04
+        - target: s390x-unknown-linux-gnu
+          os: ubuntu-24.04-s390x
         - target: thumbv6m-none-eabi
           os: ubuntu-24.04
         - target: thumbv7em-none-eabi
@@ -105,8 +109,21 @@ jobs:
       TEST_VERBATIM: ${{ matrix.test_verbatim }}
       MAY_SKIP_LIBM_CI: ${{ needs.calculate_vars.outputs.may_skip_libm_ci }}
     steps:
+    - name: Print $HOME
+      shell: bash
+      run: |
+        set -x
+        echo "${HOME:-not found}"
+        pwd
+        printenv
     - name: Print runner information
       run: uname -a
+
+    # Native ppc and s390x runners don't have rustup by default
+    - name: Install rustup
+      if: matrix.os == 'ubuntu-24.04-ppc64le' || matrix.os == 'ubuntu-24.04-s390x'
+      run: sudo apt-get update && sudo apt-get install -y rustup
+
     - uses: actions/checkout@v4
     - name: Install Rust (rustup)
       shell: bash
@@ -117,7 +134,12 @@ jobs:
         rustup update "$channel" --no-self-update
         rustup default "$channel"
         rustup target add "${{ matrix.target }}"
+
+    # Our scripts use nextest if possible. This is skipped on the native ppc
+    # and s390x runners since install-action doesn't support them.
     - uses: taiki-e/install-action@nextest
+      if: "!(matrix.os == 'ubuntu-24.04-ppc64le' || matrix.os == 'ubuntu-24.04-s390x')"
+
     - uses: Swatinem/rust-cache@v2
       with:
         key: ${{ matrix.target }}